Angle of attack control



Aug. 13, 1963 J. c. OWEN ANGLE 0F ATTACK CONTROL Original Filed July 24,1957 ATTACK ANGLE SENSING VANE INVENTOR. JOHN C. OWEN United StatesPatent 3,100,612 ANGLE 0F ATTACK CCBNTRUL John C. Owen, Grand Rapids,Mich, assignor, by niesne assignments, to Lear Siegler, Inc, SantaMonica, Calif., a corporation of Delaware Original application July 24,1957, Ser. No. 673,803, new Patent No. 2,967,679. Divided and thisapplication June 23, 1960, Ser. No. 66,393

6 Claims. (Cl. 244-47) The present invention relates to a method ofautomatically controlling an aircraft to angle of attack as averaged andsmoothed by an inertial control device and the apparatus therefor.

This patent application is a restricted application based upon patentapplication Serial No. 673,808, filed July 24, 1957, by John C. Owen,for Angle of Attack Control, now US. Patent 2,967,679.

At the present time the method for controlling an aircraft to an angleof attack involves an angle of attack sensor located on the aircraft insuch a manner as to sense the angle of attack of the aircraft relativeto the incident airflow. This sensor dictates and transmits signals,electrical or otherwise, in relation to the angle of attack at which theaircraft is flying. The sensor is usually used in conjunction with azero resetting angle of attack setting device, set either manually orautomatically for a desired pre-selected angle of attack, and deviationstherefrom by the aircraft result in signals being generated forindication and/or control purposes. in systems using -auto maticcontrol, such for example as an automatic pilot, these signalsindicating a departure from the pre-selected angle of attack 'are feddirectly into the pitch channel of the autopilot. The autopilot thenmanipulates the elevator of the aircraft and causes the aircraft to flyat the prescribed angle of attack as measured by the sensor. These samesignals may provide an indication in the aircraft from which the pilotmay manually control the aircraft to the selected angle of attack whenan autopilot is not being used.

In usual practices the control signals from the angle of attack sensorare fed more or less directly to the autopilot elevator servo channel.The elevator of the aircraft then responds directly to movements of theangle of attack sensor. Flight through turbulent lair causesconsiderable perturbations of the angle of attack sensor, theseperturbations being transmitted via the autopilot to the aircraftselevator. The result is a high degree of activity on the aircraftelevator, this activity being reflected on the control stick in thecockpit; In addition, the aircraft is proportionately active in thepitch attitude. tions can cause considerable concern to the pilot andthe passengers. Furthermore, depending on the authority allowed to theautopilot, control can become sufiiciently violent so as to damage ordestroy the aircraft.

The present invention has for its purpose the elimination of theseaforementioned deficiencies and problems heretofore encountered by usualtangle of attack control systems, by averaging the dictations of theangle of attack sensor (and angle of attack setting device) by means ofan inertial device. V

Another purpose of this invention is to eliminate the aforementionedundesirable pitching etfects of turbulence when under control of angleof attack without any sacrifice in the overall desired performance ofthe aircraft under automatic control.

A further objective of this invention is to provide a method forcontrolling the aircraft elevator to accommodate the variation orturbulence in the incident airflow to obtain smooth flight throughturbulent air While under the control of an angle of attack sensor.

These situa- A still further objective of this invention is to provide amethod for controlling an aircraft Whichis responsive to the air flow infront of the aircraft to cause the aircraft to fly on a long term basisas an aerodynamic body to a selected angle of attack, but to fly for theshort term periods of turbulence as an inertial body.

A further objective of the invention is to provide devices or apparatusfor controlling an aircraft in accordance with the desired method ofcontrol.

In the present invention there is provided an angle of attack sensorphysically located on the aircraft so as to sense the alignment of theflow of the incident air mass relative to the aircraft and generate ordictate a sensor signal. In conjunction with the angle of attack sensoris a setting device which may be operated either manually orautomatically to provide a selected angle of attack to which theaircraft and its related base signal is to be controlled. Thecombination of the sensor signal and its associated setting device orbase signal dictates an output signal which represents the departure ofthe aircraft from the selected angle of attack. An inertial device, suchfor example as a conventional vertical gyroscope or an integrating rategyroscope, or the like, properly oriented Within the aircraft, averagesthe output signal and develops an elevator control signal which is fedinto an elevator control system consisting of an amplifier and a servomotor connected to the aircraft elevator. The elevator is positioned inaccordance with control signal input to the amplifier in a manner usualwith conventional automatic pilots.

In the present invention the signals emanating from the combination ofthe angle of attack sensor and the setting device bias the gyroscope orother inertial device and the signal developed by the inertial devicecontrols the elevator servo positioning system.

For purposes of description and not of limitation, the structure forcarrying out the method may take detailed physical form as hereinafterdescribed and as illustrated in the accompanying drawing in which theonly figure represents an angle of attack control schematic of a typicaldevice of this invention.

The embodiment of the invention as illustrated in the FIGUREdemonstrates the coordination of the sensor with an automatic pilot tocontrol the elevators of an aircraft. It is understood that the sensorsignals provided by the sensor may be used to indicate needed changes tothe pilot who can manually operate the elevators when the automaticpilot is not being used. The reference character 10 refers to the angleof attack sensor which is usually positioned on the aircraft to engagethe air in advance of the aircraft. In this case, the angle of attacksensor 10 employs a synchro-type pick-off of design commonly used in theindustry and, therefore, not detailed in the drawing.

The system is also provided with an absolute angle of attack settingdevice ll which also employs a synchro, the device 11 being positionedin the cockpit of the aircraft for adjustment by the pilot orautomatically. The figure further illustrates schematically the elevator12 of the aircraft which is controlled by or manipulated by an elevatorservo 13. Power for the elevator servo 13 is dependent on the outputsignals from the sensor 10 and setting device 11 which signals are fedthrough amplifier 15 and process the pitch gyro 14 to produce an outputsignal from the latter which is then amplified by the amplifier 16. Theamplifier 15 is connected between the sensor 10 in conjunction with thesetting device 11, and the torquer 14' on the gyroscope 14-, while theamplifier 16 is interconnected between the gyroscope 14 and the elevatorservo 13.

The connection, wiring and specific physical structures used fortransmitting signals or power or for conaccounted for so that theaircraft will fly at the pilots desired angle of attack. The signals and11' from the sensor 10 and the attack setting device 11 provide signallSwhich is fed through the amplifier 15 to the torquer 14 to causeprecession of the vertical gyroscope 14 about its pitch axis 17.Conventional gravitational erection has been removed from the gyroscopeand the torquer precesses the gyroscope wheel in response to only thesignals from the amplifier 15. This precession of the gyroscope wheelprovides an output or control signal 16' from the pitch axis of thegyroscope which is fed to the elevator servo channel of the autopilot orto the elevator servo amplifier l6 and then to the elevator pitch theaircraft to null out the gyroscope pitch axis signal 16'. If theattained attitude of the aircraft does not satisfy the differentialoutput of the sensor 10 and attack setting device 11, the gyroscopecontinues to precess until that output is satisfied. When that output issatisfied, the torquers-stop processing the gyroscope so that thegyroscope maintains a fixed attitude in space and the aircraft continuesto fly oriented in pitch about this attained position of the verticalgyroscope.

Signals from the sensor as a result of turbulent air or otherperturbations are filtered out and only a relatively smooth signal isfed to the elevator channel, the turbulent signals. which wouldotherwise cause concern and possible damage being rendered harmless. Inother words, only gradual adjustment to the average angle of attack isattained. During high frequency disturbances, the aircraft is controlledby the pitch or vertical gyroscope in a normal'fashion as well known inthe field of automatic pilot systems.

It is to be noted that the major difliculties and problems heretoforeencountered have been overcome and that the objectives or" the presentinvention have been attained. With this system the desired angle ofattack may be maintained through flight in smooth or steady air. At thesame time, if the sensor encounters turbulent air conditions, the signalis trimmed or tempered by an inertial device before it is fed to theservo controlling the elevators, thereby preventing jerking or unduestraining of the mechanical parts of the plane.

It is understood that various modifications and details in thearrangements of the parts may be had Without departing from the spiritand scope of the invention as hereinafter claimed.

I claim:

1. In an angle of attack control system for aircraft having an elevatorand a signal operated actuator therefor, the combination comprising:

a desired absolute angle of attack electrical signal setting means forproviding a desired absolute angle of attack signal,

a sensor responsive to instantaneous airflow changes 4 in advance of theaircraft and providing an instantaneously changeable sensor signal,means merging said signals into an angle of attack error signal, a pitchgyroscope having a pitch axis and a pitch axis torquer biased by saidmodified angle of attack signal to precess said gyroscope about saidpitch axis,

flow having stable and varying air masses, said system comprising:

a desired absolute angle of attack electrical signal setting means,for'providin'g a desired absolute angle of attack signal, which alonerepresents the signal needed to obtain the angle of attack for stableair conditions; 7

sensor means instantaneously responsive to changes in the direction ofincident airflow and providing a sensor signal which alone representsthe signal needed to obtain the instantaneous angles of attack forvarying air conditions;

a gyroscope adapted to be biased about an axis simultaneously by both ofsaid signals and providing an output signal; and

a servo mechanism responsive to said output signal and connected to saidelevator to position the elevator to obtain the angle of attackcorresponding to said desired absolute angle of attack electricalsignal.

4. The structure as defined in claim 3 wherein said gyroscope is avertical gyroscope having a torquer'on an axis thereof connected to beresponsive to both of said signals.

5. The structure as defined in claim 3 wherein said gyroscope is anintegrating rate gyroscope.

6. An aircraft attack angle control apparatus com:

prising:

means responsive to instantaneous angle of attack and having an outputelectrical signal which is a function scope, said third signal beingconnected to control said torquing means;

angular detecting means connected to said gyroscopic means to detectprecession thereof; and

means responsive to the angle of precession of said gyroscopic means forcontrolling the angle of attack of said aircraft.

References (Zited in the file of this patent UNITED STATES PATENTSDraper et a1. July 3, 1956 Jude et a1 July 8, 1958

1. IN AN ANGLE OF ATTACK CONTROL SYSTEM FOR AIRCRAFT HAVING AN ELEVATORAND A SIGNAL OPERATED ACTUATOR THEREFOR, THE COMBINATION COMPRISING: ADESIRED ABSOLUTE ANGLE OF ATTACK ELECTRICAL SIGNAL SETTING MEANS FORPROVIDING A DESIRED ABSOLUTE ANGLE OF ATTACK SIGNAL, A SENSOR RESPONSIVETO INSTANTANEOUS AIRFLOW CHANGES IN ADVANCE OF THE AIRCRAFT ANDPROVIDING AN INSTANTANEOUSLY CHANGEABLE SENSOR SIGNAL, MEANS MERGINGSAID SIGNALS INTO AN ANGLE OF ATTACK ERROR SIGNAL,